Microbiology Final Exam Review: Comprehensive Study Guide

Microbiology Overview

Categories of Microorganisms

Microorganisms are classified into several basic categories, each with unique characteristics and domains.

• Bacteria: Single-celled prokaryotes; domain Bacteria.

• Archaea: Single-celled prokaryotes; domain Archaea.

• Fungi: Eukaryotic organisms including yeasts and molds; domain Eukarya.

• Protozoa: Unicellular eukaryotes; domain Eukarya.

• Algae: Photosynthetic eukaryotes; domain Eukarya.

• Viruses: Acellular entities; not classified in any domain.

Example: Escherichia coli is a bacterium in the domain Bacteria.

Scientific Method

The scientific method is a systematic approach to investigation.

1. Observation

2. Hypothesis formation

3. Experimentation

4. Analysis

5. Conclusion

Example: Testing whether a disinfectant kills bacteria.

Koch’s Postulates

Koch’s postulates are criteria for establishing a causal relationship between a microbe and a disease.

1. The microorganism must be found in all cases of the disease.

2. It must be isolated and grown in pure culture.

3. The cultured microbe must cause disease when introduced into a healthy host.

4. It must be re-isolated from the experimentally infected host.

Importance: Foundation for identifying pathogens. Pitfalls: Some pathogens cannot be cultured; some diseases are caused by multiple organisms.

Cell Structure and Function

Prokaryotic vs Eukaryotic Cells

Understanding cell structure is fundamental in microbiology.

• Prokaryotes: No nucleus, simple organelles, include Bacteria and Archaea.

• Eukaryotes: Nucleus, complex organelles, include Fungi, Protozoa, Algae.

Similarities: Both have plasma membranes, cytoplasm, ribosomes. Differences: Eukaryotes have membrane-bound organelles; prokaryotes do not.

External Structures of Bacterial Cells

• Glycocalyces: Protective layer; capsule or slime layer.

• Flagella: Motility structures.

• Fimbriae and Pili: Attachment and conjugation.

Bacterial Cell Walls: Gram-Positive vs Gram-Negative

Cell wall structure determines staining and antibiotic susceptibility.

• Gram-Positive: Thick peptidoglycan, teichoic acids.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS).

Example: Staphylococcus aureus is Gram-positive; Escherichia coli is Gram-negative.

Cytoplasm of Bacteria

• Cytosol: Fluid component.

• Inclusions: Storage granules.

• Endospores: Resistant structures for survival.

• Nonmembranous Organelles: Ribosomes.

Eukaryotic Cell Structures

• Glycocalyces: Cell surface protection.

• Cell Walls: Found in fungi, algae.

• Cytoplasmic Membranes: Phospholipid bilayer, fluid mosaic model.

• Flagella, Cilia: Motility and movement.

• Membranous Organelles: Nucleus, mitochondria, ER, Golgi.

Mechanisms of Transport Across Membranes

• Passive Transport: Diffusion, facilitated diffusion, osmosis.

• Active Transport: Requires energy (ATP).

Phospholipid Bilayer: Composed of hydrophilic heads and hydrophobic tails. Fluid Mosaic Model: Proteins float in or on the fluid lipid bilayer.

Tonicity

Tonicity describes the effect of a solution on cell volume.

• Isotonic: No net movement of water.

• Hypertonic: Water leaves cell; cell shrinks.

• Hypotonic: Water enters cell; cell swells.

Microbial Nutrition and Growth

Terms Relating to Microbial Growth

Microbes are classified by their energy and carbon sources.

• Photoautotroph: Light energy, CO2 as carbon source.

• Chemoautotroph: Chemical energy, CO2 as carbon source.

• Photoheterotroph: Light energy, organic carbon.

• Chemoheterotroph: Chemical energy, organic carbon.

Oxygen Requirements:

• Aerobe: Requires oxygen.

• Anaerobe: Does not require oxygen.

• Obligate: Strict requirement (aerobe or anaerobe).

• Facultative Anaerobe: Can grow with or without oxygen.

• Aerotolerant Anaerobe: Tolerates oxygen, does not use it.

Temperature Preferences:

• Psychrophile: Cold-loving.

• Mesophile: Moderate temperature.

• Thermophile: Heat-loving.

• Hyperthermophile: Extreme heat.

• Barophile: Pressure-loving.

Microscopy

Types of Microscopes

Microscopes are essential for visualizing microorganisms.

• Light Microscopes: Use visible light; includes brightfield, darkfield, phase-contrast.

• Electron Microscopes: Use electron beams; includes transmission (TEM) and scanning (SEM).

Example: TEM provides high-resolution images of internal cell structures.

Microbial Metabolism

Key Terms and Processes

Metabolism encompasses all chemical reactions in a cell.

• Catabolism: Breakdown of molecules; releases energy.

• Anabolism: Synthesis of molecules; requires energy.

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative Phosphorylation: ATP generated via electron transport chain.

• Photophosphorylation: ATP generated using light energy.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Enzyme: Biological catalyst.

• Substrate: Molecule acted upon by enzyme.

• Photosynthesis: Conversion of light energy to chemical energy.

• Amphibolic: Pathways that are both catabolic and anabolic.

• Proton Gradient: Drives ATP synthesis.

• Electron Transport Chain: Series of electron carriers.

• Active Site: Region of enzyme where substrate binds.

• Electron Carrier: Molecule that transfers electrons (e.g., NAD+, FAD).

Equation:

$\text{ADP} + \text{P}_i \rightarrow \text{ATP}$

Controlling Microbial Growth in the Environment

Terminology of Microbial Control

Understanding terms is crucial for discussing microbial control.

• Sterilization: Removal of all microbes.

• Aseptic: Free of pathogens.

• Disinfection: Removal of pathogens from surfaces.

• Antisepsis: Removal of pathogens from living tissue.

• Degerming: Removal of microbes by mechanical means.

• Sanitization: Reduction of microbes to safe levels.

• -static/-stasis: Inhibits growth.

• -cide/-cidal: Kills microbes.

Chemical Methods of Microbial Control

Various chemicals are used as antiseptics and disinfectants.

• Phenol and Phenolics: Disrupt cell membranes; effective against bacteria.

• Alcohols: Denature proteins; effective against bacteria and fungi.

• Oxidizing Agents: Oxidize cellular components; e.g., hydrogen peroxide.

• Surfactants: Lower surface tension; e.g., soaps.

• Aldehydes: Cross-link proteins; e.g., formaldehyde.

• Enzymes: Break down cell walls.

• Halogens: Oxidize proteins; e.g., chlorine, iodine.

• Heavy Metals: Inactivate proteins; e.g., silver, mercury.

Controlling Microbial Growth in the Body: Antimicrobial Drugs

Key Definitions

• Antimicrobial agents: Chemicals that kill or inhibit microbes.

• Antibiotics: Naturally produced antimicrobial agents.

• Narrow-spectrum: Effective against specific microbes.

• Broad-spectrum: Effective against many microbes.

Tests for Effectiveness

• Diffusion Susceptibility Test (Kirby-Bauer): Measures zone of inhibition to assess drug effectiveness.

Mechanisms of Action of Antimicrobials

Antimicrobials target specific cellular processes.

Drug	Mechanism of Action	Effective Against
Penicillin	Inhibits cell wall synthesis	Gram-positive bacteria
Bacitracin	Inhibits cell wall synthesis	Bacteria
Tetracycline	Inhibits protein synthesis	Broad-spectrum
Sulfonamide	Inhibits folic acid synthesis	Bacteria
Actinomycin	Inhibits RNA synthesis	Bacteria
Streptomycin	Inhibits protein synthesis	Bacteria
Quinolones	Inhibit DNA gyrase	Bacteria

Terms Relating to Microbial Growth

• Autoclave: Device for sterilization using steam under pressure.

• Selective Toxicity: Drug targets pathogen, not host.

• Synergism: Combined effect greater than sum.

• Antagonism: Combined effect less than sum.

• Nucleotide/Nucleoside analog: Mimics DNA/RNA building blocks; disrupts replication.

Microbial Genetics

Genetics of Prokaryotes vs Eukaryotes

• Gene: DNA segment coding for a product.

• Genome: Complete genetic material.

• Nucleotide: DNA/RNA building block.

• Plasmids: Extra-chromosomal DNA in prokaryotes.

• Base pairs: A-T, G-C in DNA.

DNA Replication: Semi-conservative process; leading and lagging strands.

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Central Dogma: Information flows from DNA to RNA to protein.

Key Enzymes and Terms

• Primer: Short RNA for initiation.

• Primase: Synthesizes primer.

• Helicase: Unwinds DNA.

• Gyrase: Relieves supercoiling.

• DNA Polymerase: Synthesizes DNA.

• RNA Polymerase: Synthesizes RNA.

• Codon: Three-base sequence in mRNA.

• Anticodon: Three-base sequence in tRNA.

• tRNA: Transfers amino acids.

• Operon: Group of genes regulated together.

• Promoter: DNA region for transcription initiation.

• Mutation: Change in DNA sequence.

• Mutagen: Agent causing mutation.

Gene Transfer Mechanisms

• Conjugation: Transfer via pilus.

• Transformation: Uptake of naked DNA.

• Transduction: Transfer via bacteriophage.

Okazaki Fragments: Short DNA segments on lagging strand.

Selection Methods

• Positive Selection: Direct identification of mutants.

• Negative/Indirect Selection: Identifies mutants by absence of function.

Phage and Restriction Enzymes

• Phage (Bacteriophage): Virus infecting bacteria.

• Restriction Enzymes: Cut DNA at specific sequences.

PCR and Recombinant DNA Technology

• PCR: Amplifies DNA.

• Recombinant DNA Technology: Manipulation of DNA for research, medicine, industry.

Viruses and Prions

Structures and Types

• Viruses: Acellular, DNA or RNA genome, protein coat.

• Prions: Infectious proteins; cause neurodegenerative diseases.

Example: Influenza virus (RNA virus); prion causes Creutzfeldt-Jakob disease.

Infection, Infectious Diseases, and Epidemiology

Symbiotic Relationships

• Mutualism: Both benefit.

• Parasitism: One benefits, one harmed.

• Commensalism: One benefits, other unaffected.

• Amensalism: One harmed, other unaffected.

Pathogens and Reservoirs

• Pathogen: Disease-causing microbe.

• Opportunistic Pathogen: Causes disease in compromised hosts.

• Reservoirs: Sources of infection: human, animal, nonliving.

Transmission and Disease Process

• Parenteral Route: Entry via breaks in skin.

• Fomites: Inanimate objects transmitting disease.

• Vector: Living organism transmitting disease.

Disease Process:

• Incubation

• Prodromal

• Illness

• Decline

• Convalescence

Virulence and Pathogenicity

• Virulence: Degree of pathogenicity.

• Pathogenicity: Ability to cause disease.

• Exotoxin: Secreted toxin.

• Endotoxin: LPS component of Gram-negative bacteria.

• Lipid A: Toxic part of LPS.

Immunology

Innate and Adaptive Immunity

The immune system protects against pathogens via innate and adaptive mechanisms.

• Innate Immunity: Non-specific, first and second lines of defense.

• Adaptive Immunity: Specific, cell-mediated and humoral responses.

Cell-Mediated Immunity: T cells (CTL, Thelper). Humoral Immunity: B cells, plasma cells, antibodies.

Antibody Types and Functions

• IgG: Main antibody in blood.

• IgM: First antibody produced.

• IgA: Found in mucosal areas.

• IgE: Involved in allergies.

• IgD: B cell receptor.

Immunity Types

• Passive: Antibodies from another source.

• Active: Own immune response.

• Artificial: Vaccination.

• Natural: Infection or maternal antibodies.

Complement System

Proteins that enhance immune responses.

Symptoms vs Signs

• Symptoms: Subjective (felt by patient).

• Signs: Objective (measured by observer).

Immune Cells

• Basophils: Release histamine.

• Eosinophils: Combat parasites.

• Neutrophils: Phagocytosis.

• Macrophages: Phagocytosis and antigen presentation.

Immune Disorders

Overview

Immune disorders include hypersensitivity, autoimmunity, and immunodeficiency. Refer to class slides and notes for details.

Additional info: Some content was expanded for clarity and completeness based on standard microbiology textbooks.